1. Field of the Invention:
This invention relates to an image analysis system for performing a variety of measurements and more specifically to an image analysis system for performing measurements on single or multiple features at any orientation in a field of view.
2. Description of the Prior Art:
In image analysis, it is necessary to extract geometric data from images having varied shape, size and light intensity, which data identifies a variety of materials or objects. This is done by using means, such as those outlined in U.S. Pat. No. 3,763,357, entitled "THRESHOLD CIRCUIT FOR CONVERTING A VIDEO SIGNAL TO A BINARY VIDEO SIGNAL" issued Oct. 2, 1973 for inventor Roger R. A. Morton, wherein a television camera scans the image to be measured and a threshold circuit defines the boundary of the image of an object by producing a signal containing information relating to scan line intercepts of the objects or features to be measured. A feature can comprise any object, cell, lake, island, or two or three dimensional objects which can be imaged onto a television camera to be ultimately measuring using image analysis techniques.
The basic processes of image analysis are to form images of specimens or objects to be measured. Such images will contain features having a gray value or light intensity different from their background. By scanning each image along parallel line scans, to produce a video signal whose amplitude is a function of the brightness or intensity of the image at each point along the parallel scan line, a video signal is produced. This vidio signal is then analyzed to determine the boundaries of features to be measured. The distance or segment of a scan line which intercepts the feature is termed, "an intercept". Thus, the end points of any intercept occur at the boundary of a feature. Obviously, any feature which subtends more than one line will have associated with it, a group of intercepts which taken as a whole for that feature, represents the boundaries of the feature.
The measurement of features is generally associated with determining geometric parameters such as area within for boundary, perimeter around the boundary, or longest dimension across the feature. In image analysis it is important to be able to perform a variety of different measurements on features depending on the specific feature whether it be, for example, a particle or a metallurgical inclusion. These different measurements relate to different physical properties of the feature. Furthermore, by combination of different measurements, shape factors, orientation factors, as well as derived measurements, may be extracted to more exactly describe the feature.
A number of techniques for performing measurements on features exist. Examples include the measurement of area on a selected feature as outlined in U.S. Pat. No. 3,805,028 entitled "METHODS OF AND APPARATUS FOR DETERMINING THE QUANTITY AND PHYSICAL PARAMETERS OF OBJECTS", issued Apr. 16, 1974 for inventor Roger R. A. Morton and the measurement of total area as outlined in U.S. Pat. No. 2,494,441 entitled "METHOD AND APPARATUS FOR ELECTRONICALLY DETERMINING PARTICLE SIZE AND DISTRIBUTION", issued Jan. 10, 1950 for inventor James Hillier. Measurement of longest dimension, as outlined in U.S. Pat. No. 3,805,028 entitled "METHODS OF AND APPARATUS FOR DETERMINING THE QUANTITY AND PHYSICAL PARAMETERS OF OBJECTS", issued Apr. 16, 1974 for inventor Roger R. A. Morton is also known. However, the technique outlined therein requires substantially more electronic circuitry when measuring, for example, tangent to tangent distances, or Feret's diameter at any precisely defined angles to the line of scan. The present invention is however able to perform Feret's diameter at any precisely defined angle. Patents, such as U.S. Pat. No. 3,244,810 have disclosed methods for obtaining the maximum chord of a feature or a chord in a given direction. These measurements are not geometrically the same as Feret's diameter or longest dimension.
In the present invention perimeter is defined as the total length of the boundary of a feature, including the length of the boundaries of the holes of the feature. Convex perimeter is the perimeter of the smallest convex region which escribes the feature being measured or, alternatively, it can be thought of as the distance required to wrap a piece of string one full revolution around the outside of a feature boundary. Feret's diameter, also termed tangent to tangent distance, is the distance between extreme parallel tangents to the feature, such distance being measured at an angle perpendicular to the tangents. When defined at a specific orientation, the Feret's diameter is defined by the angle of the distance between the parallel tangents, such angle being measured with respect to the horizontal direction.
Longest dimension is a maximum tangent to tangent distance, or maximum Feret's diameter determined over Feret's diameters measured at all orientations with respect to the feature.
Breadth is the minimum Feret's diameter or the minimum of all Feret's diameters measured at all orientations to the feature. It is the smallest distance between extreme parallel tangents to the feature regardless of orientation. Projected length corresponds to the Feret's diameter, plus the distance across any holes or re-entrances in the direction that the Feret's diameter is being measured.
Previous patents, such as U.S. Pat. No. 3,216,311 entitled "NON-CONTACTING OBJECT MEASURING APPARATUS", issued Nov. 9, 1965 for inventors Robert J. Bibbero, Abraham Mann and Arnold K. H. Goldberger have disclosed techniques for determining the maximum distance subtended by a chord across a feature from parallel scan line intercept signals, by mechanically rotating the image. The chord is a measurement which differs geometrically from the measurements disclosed herein, and furthermore, techniques disclosed herein do not require the rotation of the image with respect to the scan direction.
U.S. Pat. No. 3,244,810 entitled "INTERCEPT SCANNING SYSTEM", issued Apr. 5, 1966 for inventor David A. Williams discloses techniques for measuring chords at predetermined orientations to the scan lines. However, the chord measurement is geometrically different from the distance between tangents. U.S. Pat. No. 3,740,468 entitled "FEATURE PARAMETER MEASUREMENT BY LINE SCANNING", issued June 19, 1973 for inventors Gerald M. Gardner, Saffron Walden and David W. Gibbard discloses a method for obtaining perimeter of a feature using an approximation technique involving extensive hardware.